1909] LEAVITT—HOMOEOSIS IN PLANTS 61 



from 



mbryo sac to a somatic cell in Hieracium flagellare. The 



formed norm 



ber of cases this structure aborts. A neighboring cell, which may 



be situated in the epidermis of the nucellus or in the chalazal region 



or in the integument, takes upon itself the function of a megaspore, 



though without reduction of the chromosome number. This cell 



enlarges to form an embryo sac. Its nucleus divides as that of 



the megaspore would do ; egg apparatus and antipodals are formed ; 



and even polar nuclei fuse to form an endosperm nucleus. The 



gametophyte is thus reproduced, after the failure of the proper organ 



to construct it, by a cell of the sporophytic generation. And this 



homoeotic process is habitual, hereditary, and established in the 

 species. 



podiu 



formation 



and its near allies to a homoeotic origin. The gemmae— detachable 

 shoots— arise in exactly the position of leaves, from which in their 

 earliest stages they are indistinguishable. 



The form of homoeosis most often entering into the diversifica- 

 tion of species of plants is apparently that which has above been 

 called entropy Abscission of leaflets has already been discussed 

 m t is connection. Another seemingly homoeotic feature of com- 

 pound leaves is found in their stipels. An examination of stipels 

 £ a consid erable number of groups— as in Xanthoxylum, Staphylea, 



DolT 1115 ' T . Urpinia ' Robinia > Bradburya, Desmodium, Galactia, 



c olus, Vigna, Amorpha, Sambucus— strongly suggests that the 



jpe s have arisen as echoes of the antecedent structures, stipules, 



establ' h thC eV ° lution of the leaf suita ble conditions have been 

 littl H V y occur in plants possessing stipules, and with 



uur „^ r* , alreaci y in possession of them before leaf-compound- 

 as far as one can see; when 



21 S f in ; they are generally useless, 

 m ey have a visible „«> .♦ :« * 



much 



sible use it is the same as that of the stipules, in a 

 weakened degree; they follow punctiliously the greatly vary- 



43 B <*-Tidsskrift 28:150 

 43 B <*-Zeit. 30:841. i8 72 . 



1907 



